Whether it be the sweet smell emanating from the bakery next door or the signature scent of a loved one, your nose is responsible for the rewarding rush that is felt not too long after. But with finals week in full force, what if I told you your nose was capable of rewarding you with the sweetest gift of them all? Yep, you guessed it. An 'A' on your exam. The olfactory system is the machinery behind those sweet smells I mentioned at first and for years, that was mostly all it was known to do. That is, up until the year 2007, when researchers Rasch et al. began investigating whether or not odors had an influence on memory consolidation. To their surprise, the results of this landmark study gave concrete evidence that odors do in fact, play a role in the retention of memory. How is this possible, you may ask? And more importantly, how are you going to use this information to get that 'A'?
In the paper "Scents and Reminiscence: Olfactory Influences on Memory Consolidation in the Sleeping Human Brain researchers Shanahan et al. further investigated the process known as Olfactory Targeted Memory Reactivation (TMR). The researchers first looked at the previously mentioned study conducted by Rasch et al. in 2007. In this study, participants were exposed to a rose odor that was coupled with a visuospatial learning task. This learning task required participants to memorize card locations. The rose odor followed a 30-second alternating pattern where it was either on or off, in order to prevent the subjects from developing a tolerance to the odor. Following the learning task, participants were then asked to sleep. After the participants had awakened, they were asked to recall card locations they had previously studied during the day. Shockingly, Rasch et al. discovered that for participants who had been exposed to the rose odor during slow-wave sleep (SWS), there was an observable higher recollection of memory on the learning task. Furthermore, the researchers concluded that these results must be specific to SWS mainly due to the fact that participants who had been exposed to the odor during REM sleep showed no signs of memory retention on the learning task. The results from the 2007 Rasch et al. study presented in Shanahan's article were crucial in highlighting the existing relationship between odor cues and memory consolidation.
Similarly to the work presented by Shanahan et al., a newsletter written by Tim Newman titled "Using smells to boost learning during sleep" for Medical News Today details a newly conducted study that aimed to investigate whether the results observed in the Rasch study were able to translate in an experiment outside of the laboratory. The experiment consisted of 54 sixth-grade students from Germany. In order to couple learning with an odor, the participants were provided with rose sticks and were instructed to keep the rose sticks close as they studied English vocabulary for an upcoming exam. It is important to note that not all of the students were exposed to the rose sticks. In fact, researchers had previously split half of the 54 students into 4 experimental groups, each with a different set of conditions. The first group had no exposure to odor, the second was exposed to the rose stick odor both at home and while taking the exam, the third group was exposed to the odor during learning and every night before the exam but not during the actual exam, and the fourth group was exposed to the odor both during learning and every night before the exam, as well as during the exam. The other half of students acted as controls, since they were not exposed to the odor cues at any point in time. In parallel to the results observed in the Rasch et al. study, the researchers for this experiment discovered that students in groups 3 and 4 performed much better on the vocabulary exam than did the students from groups 1 and 2. These results further reinforce the relationship between exposure to odor cues during sleep and memory consolidation. However, perhaps the most interesting aspect of this study was that the odor cues were administered throughout the entire night, not just during SWS. Although the sample size of 54 students is not large enough to draw an absolute, these results may be indicative of odor exposure not being specific to SWS, as Shanahan et al. had previously concluded.
With that being said, the two articles were effective in emphasizing the effects of exposure to odor cues during sleep on memory consolidation. As seen in the Newman article, the translation of results from the laboratory to a real-life setting is attainable. Identifying the conditions through which the results proved to be beneficial gives us, as students, an insight into what may become the next avenue for effective studying. As for the curious minds who may still be wondering how this is possible, the Shanahan et al. paper presents fMRI data that highlights the ability of odors presented during SWS to activate the left hippocampus. With the semester coming to a close and studying demanding more time out of your day as exams approach, it may be in your best interest to pick up a rose stick and try out the methods described in the Newman article. Because yes, your nose might just get you that 'A'.
References
Shanahan, L.K., Gottfried, J.A. (2017). Scents and Reminiscence: Olfactory Influences on Memory Consolidation in the Sleeping Human Brain. In: Axmacher N., Rasch B. (eds) Cognitive Neuroscience of Memory Consolidation. Studies in Neuroscience, Psychology and Behavioral Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-45066-7_20
Newman, T. "Using smells to boost learning during sleep". Medical News Today, 8 February 2020, https://www.medicalnewstoday.com/articles/using-scents-to-boost-learning-during-sleep
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